In the last two years, the unstoppable juggernaut that is Call of Duty has begun to attract negative mutterings. According to the cynics, it has become samey, perhaps falling into a tried-and-tested comfort-zone. Activision, clearly, has heeded such whisperings, and had a word with developer Treyarch.

And the result is that the next iteration of the insanely popular first-person shooter, Call of Duty: Black Ops 2, will dare to break the rigid mould of its predecessors, adding branching storylines, gameplay choices and even sandbox-style missions to its single-player game.

Combined with a leap from the Cold War to the near future, Treyarch's strand of the huge-selling franchise, at least, looks set to receive an invigorating jolt just when it was in danger of slipping into comfortable somnolence.

At E3 2012, Activision and Treyarch showcased two of the game's missions, and while they preserved CoD's Hollywood action-style vibe, both markedly diverged from CoD's usual single-path inevitability.

The first one was the more conventional: a typically blockbusting and spectacular story mission, in which you and your squad (in 2025, when the game is set), are escorting the (female) US president to a meeting at the Bonaventure Hotel in Downtown Los Angeles (in real life, a stone's throw from the LA Convention Centre where E3 takes place).

Ambushed on the freeway (anyone who has ever been to LA more than once should know to steer well clear of the freeways in the vicinity of Downtown), your armoured vehicle hits an ambush – suddenly, helicopters are crashing around and over you, motorbikes are being catapulted to the ground level far below, and you and your party must proceed on foot.

Amid the typical welter of chaos and gunfire – atmospherically speaking, Black Ops 2 throws kitchen-sink intensity at you, as is customary – your first task is to jump into another crashed vehicle and man a Stinger missile battery, in order to take down incoming hostile aircraft.

Providing a first glimpse of the futuristic weaponry that Black Ops 2's 2025 setting allows Treyarch to have fun with, it was highly automated – you basically had to move it around until target-locks were achieved on incoming waves of fighter-planes, before unleashing a barrage of missiles.

The next portion of the mission introduced the element of choice which, while commonplace in other first-person shooters, is a first for CoD. Regrouping with your squad at the edge of the destroyed freeway, you're offered the option – simply by moving to different points – of staying on the freeway and providing sniper cover, or rappelling down to ground level for some more conventional CoD thick-of-the battle action.

Choosing to snipe, another futuristic weapon was unveiled – a sniper with a scope that could heat-sense through metal and concrete, with the kick of a mule. We took out incoming enemies (directed to an extent by those on the ground) before rejoining the rest of the squad, proceeding with the president in tow on foot. General banter revealed that the villain behind the attack was called Menedez, and he had apparently achieved some sort of control over at least part of the US Army.

All the while, the squad had been in contact with a woman called Anderson, flying an FA-38 hover-jet and providing air support. After commandeering another vehicle – cueing a sequence of on-rails shooting – another assault saw Anderson landing, before one of the LA Downtown skyscrapers came crashing down.

With Anderson knocked out, it was up to us to jump into the FA-38, and fly around (again, a simple task of steering and targeting, with the computer controlling height-variations, making it much less fiddly to fly than, for example, the planes in Battlefield), taking out incoming planes. We ended up back on foot, amid an impressively wrecked Downtown LA – a fate that many would wish on one of the most unloved areas of the mega-city.

Away from the story and into the sandbox

Call of Duty: Black Ops 2 Photograph: Foo1;Foo2

Next up was a so-called Strikeforce mission – a complete (and therefore welcome) departure from anything we've seen in the single-player element of a CoD game before. Indeed, it was much more reminiscent of the game's multiplayer side.

Treyarch explained that is one of a number of missions that exist away from the main storyline arc, which can choose to play whenever you want. Not that they are totally separate – the single-player game's ending will vary according to whether you succeed or fail in the Strikeforce missions.

And, for the first time in CoD, the Strikeforce missions (which are squad-based, so you have to work to keep at least some squad-members alive) introduce the concept of failure – no longer is it a case of merely respawning when you die.

Set in Singapore's docks, the mission (entitled Keppel Terminal) set you and your squad the objective of working your way to a container ship, calling in an airstrike and destroying it. How you chose to achieve that was entirely up to you.

You could take a completely hands-off approach, zooming out to an Overwatch view, setting waypoints for your squad (according to what enemies were incoming), and spawning items like machine-gun-equipped quad-copters, battlefield drones and the like to help them. Or you could zoom into any soldier or piece of battlefield kit and take direct control.

Keppel Terminal may have lacked the cinematic Michael Bay spectaculars of the story missions, but it was every bit as intense, with waves of enemies and all the futuristic battlefield toys that you had access to thrown right back at you. The demonstrator jumped into battlefield drones, quad-copters and the like, and powered through multiple objectives, such as taking out missile defence systems in order to facilitate the air-strike at the end.

What was striking about Keppel Terminal – and presumably extends to all the Strikeforce missions – was that it required a strategic approach. Which, of course, has always been a feature of the various CoD games' more sophisticated and elaborate multiplayer modes, but has never impinged on the single-player game – you've always been told what to do and where to go in the past.

If people still exist who play CoD strictly offline, the Strikeforce missions will introduce to the joys of online play. With the added bonus of adding a random element to the ending you'll get, which in turn adds another layer of replay value.

Black Ops 2, then – even on the evidence of a mere two missions – adds a vast amount of gameplay diversity to the CoD blueprint, addressing the biggest recent criticism of the franchise. And it does so without letting the sometimes excruciating levels of intensity slip, even for a moment.

In the past, Treyarch has been seen as the least talented of the two developers who take yearly turns at churning out CoD games, but it had to step up to the plate when Infinity Ward suffered its well-publicised meltdown. The added responsibility, it seems, suits it. If the rest of Black Ops 2 turns out as well as the two missions we saw, Infinity Ward will do well to match it.

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